The present invention relates to an improved design for a Michelson interferometer and more particularly to an apparatus for precision movement of a movable mirror in a Michelson interferometer.
Michelson interferometers are used in spectrometers which provide spectroscopic data such as light wavelength, line position, intensity and absorption coefficient. A typical Michelson interferometer employs a half-silvered mirror or beam splitter, placed at a 45.degree. angle with respect to the electromagnetic radiation being measured. The beam splitter divides the radiation into two parts, and each part is directed along a separate perpendicular path within the interferometer. One part of the radiation is reflected off of a fixed mirror. The other part is reflected off of a movable mirror. The two parts are then recombined at the beam splitter and optically interfere with each other to a degree proportional to their phase displacement. The phase displacement between the two parts is generated by the inequality in the path lengths between the movable mirror and the fixed mirror.
In a Michelson interferometer the alignment of the movable mirror must be maintained to a very high degree of precision as it travels toward and away from the beam splitter. In particular, the movable mirror should be able to move over a distance or stroke length of several centimeters while tilting less than a few arc-seconds.
State of the art Michelson interferometers use either air bearings or mechanical pivot-type bearings which require costly close tolerance machining and assembly for controlling the tilt of the movable mirror as it moves. Air bearings, such as those described in U.S. Pat. No. 3,936,193, offer higher performance but are expensive and require an air compressor and filter to supply compressed air. Mechanical pivot-type bearings, such as those described in U.S. Pat. Nos. 3,984,190 and 4,828,367, have certain limitations. Bearings of this type can have errors in the mirror alignment as the mirror moves. These alignment problems worsen at long stroke lengths, thus limiting the stroke length and system resolution. Moreover, these bearings are subject to wear and degradation. The mechanical bearings also have poor damping and tend to capture or generate mechanical and acoustical vibrations, thereby causing noise in the system output data.